Two-component developer is widely used in development devices for electrophotographic image forming apparatuses. In development devices, developer is carried on a developer bearer, and a developer regulator adjusts the amount of developer carried on the developer bearer. Then, the developer is transported to a development range facing a latent image bearer (e.g., a photoreceptor) as the developer bearer rotates. At that time, the developer is subject to centrifugal force or airflow inside the development device, and it is possible that the developer (i.e., carrier particles or toner particles) is scattered inside or outside the development device. Therefore, various approaches have been tried to prevent scattering of developer.
If developer scatters outside a development casing, it is possible that the developer adheres to the latent image bearer upstream from the development range in the direction in which the latent image bearer rotates, resulting in contamination inside the image forming apparatus. Therefore, typically a sheet to prevent scattering of developer (hereinafter “scattering prevention sheet”) is provided to fill in a clearance between the rim of the development casing adjacent to the opening (i.e., an opening rim) and the surface of the latent image bearer on the upstream side in the direction of rotation of the latent image bearer, thereby preventing scattering of developer. Although such a sheet is effective initially, the developer eventually adheres to a surface of the sheet facing the developer bearer and accumulates thereon. Upon an impact, the accumulating developer can drop and degrade image quality.
In view of the foregoing, for example, JP-2004-317567-A proposes providing a sheet to cover a developer layer downstream from the developer regulator (hereinafter “accumulation prevention sheet”), thus preventing accumulation of developer, in addition to the scattering prevention sheet. An end of the accumulation prevention sheet is fixed to an inner wall of the development casing, and another end of the sheet is not fixed (i.e., a free end) but in contact with an end of the scattering prevention sheet.
This configuration can prevent the developer from adhering to the surface of the scattering prevention sheet facing the developer bearer. Even if the developer adheres to the accumulation prevention sheet, the developer carried on the developer bearer slides on the surface of the accumulation prevention sheet facing the developer bearer, thereby inhibiting accumulation of developer thereon.
To fix the developer accumulation prevention sheet, an edge face thereof is in contact with the developer scattering prevention sheet.
Additionally, various approaches have been tried to prevent scattering of toner around the developer bearer (e.g., development roller) inside the development device. For example, to prevent toner that has left the development roller from scattering outside the development device, an insulative seal member is provided around the development roller. Alternatively, airflow is generated to prevent scattering of toner.
For example, the development roller is covered with a seal member extending in the longitudinal direction of the development roller, and an edge face of the seal member is in contact with the photoreceptor disposed facing the development roller. In such configurations, the seal member that covers the portion of the development roller exposed from the development casing may be curved into an arc, and an insulative member such as a urethane sheet is provided at an end of the seal member in contact with the photoreceptor.
The arc-shaped seal member and the urethane sheet, however, tend to be electrically charged due to friction with toner, and toner can adhere to them. If the toner falls from the arc-shaped seal member or the urethane sheet under its own weight or upon an impact, it can degrade image quality or contaminate the interior of the apparatus.
To prevent accumulation of electrical charges, for example, in JP-2005-201943-A, the side of the seal member facing the development roller is constructed of an electroconductive member that is grounded.